Current radio voice messaging systems utilize digital speech compression prior to transmission and digital speech decompression techniques after reception to conserve transmission time. Such systems also utilize a digital address and call set-up signal, followed by an analog signal for transmitting the compressed voice message to a receiver. Because the voice message is sent as an analog signal, the call set-up information typically is sent only once and applies to the whole voice message.
One of the parameters sent in the call set-up signal is the segment size, a parameter utilized by a decompression algorithm in the receiver. The segment size parameter is determined from pitch period characteristics of the voice message. To reduce latency, prior art voice messaging systems have examined only a first portion, e.g., first 2 seconds, of the voice message to estimate the pitch period of the entire message. In addition, prior art systems estimated the pitch period by calculating the average pitch period of the first portion.
The prior art techniques have resulted in two problems. First, by examining only the first portion of the message, changes in pitch period which can occur after the first portion of the message are not considered in estimating the pitch period of the message. Second, by calculating the average pitch period, even some sections of the first portion of the message can exhibit a pitch period much different from the average pitch period. These problems can produce undesirable artifacts in the decompressed message.
Thus, what is needed is a method and apparatus that can overcome the problems that have resulted from the use of the prior art techniques. Changes that occur both during and after the first portion of the message need to be considered in determining the pitch period used for compressing and decompressing the message. Preferably, this will be accomplished without a significant increase in latency.